Pulse delay system



Aug. 23, 1949.

' R. C. MOORE PULSE DELAY SYSTEM Filed April 29, .1944

Evie/j 6. 17007 his AW .5

Patented Aug. 23, 1949 PULSE DELAY SYSTEM Robert C. Moore, Philadelphia,Pa., mesne assignments, to Philco assignor, by Corporation,

Philadelphia, Pa, a corporation of Pennsylvania Application April 29,1944, Serial No. 533,385

7 Glaims.

This invention relates to pulse delay systems and particularly to pulsedelay systems in which the interval between the applied pulse and theoutput pulse is adjustable.

There are numerous occasions in the art of electronics when it isdesired to utilize the eifect of a pulse at some predetermined timeafter the occurrence of the pulse. Furthermore, it is often desirablethat the interval between the initial pulse and the delayed pulse beadjustable over a wide range.

It is therefore an object of the present invention to provide by meansof a novel circuit, a sy--- tem in which the interval between theapplied pulse and the output pulse may be easily and effectively variedover a wide range.

This and other objects and features of the invention will be understoodfrom the following description and the accompanying drawings, in which:

Fig. 1 illustrates schematically the preferred embodiment of the circuitof the present invention;

Fig. 2 is an explanatory diagram showing the wave forms ofcurrent andvoltage at various points of the system for a cycle of operation; and a1 Fig. 3 shows an alternative portion of the circuit of Fig. 1.

Referring now to Fig. 1, there is shown schematically the preferredcircuit arrangement of this invention. This circuit may be considered asa modified form of a conventional cathodeloaded multivibrator in whichT1 and T2 represent the two electron discharge devices. While T1 and T2are shown as separate vacuum tubes, and as triodes, it is evident thatboth sets of electrodes may be enclosed in a single envelope, and thatmulti-electrocle tubes other than triodes may be used in the circuitwith the conventional circuit modifications. The cathodes of tubes T1and T2 are connected together and grounded through the common cathoderesistors II] and II, resistor II being shunted by an inductance I2 toform a differentiating circuit whose function will be describedhereinafter. The anode potential for tube T1 is obtained from a suitabledirect current source B+ and is applied through resistor I3 and theresistance of potentiometer I4. Resistor I 3 may be a separate elementas shown, or it may be included in potentiometer I4, depending upon thedesired operating conditions. Vacuum tube T2 derives its anode potentialfrom the source 3+ through the current limiting resistance I5. A by-passcondenser I6 is connected embodiment of a between the anode of tube T2and ground. To the grid of tube T1 there is connected a conventionalinput circuit, comprising coupling condenser I1 and grid resistor I8.The grid of vacuum tube T2 is coupled to the plate of tube T1 throughtwo serially connected resistance-capacitance networks [9 and 20.Network I9 is composed of a'condenser 2i shunted by the total resistanceof a resistor 22 in series with that portion of potentiometer resistanceI4 between the movable contact arm 23 and the plate of tube T1. Theresistance-capacitance network 20 comprises a condenser 24 in shuntwithresistor 25. The input and output terminals of the system are shown at26 and 27 respectively.

The multivibrator utilized for the present invention diifers from themore conventional multivibrator oscillators in that it is constructedand. arranged to produce only one cycle of oscillation in response to agiven input pulse. Such single-cycle operation is not new, per se, butthis mode ofoperation is utilized in the practice of the presentinvention. 7

The operation of the system will now be described with particularreference to Fig. 1, and to the voltage and current wave forms shown inFig. 2.

In the absence of an input signal tube T2 is conducting, since a smallpositive potential is applied to its control grid from the plate circultof tube T1 through resistors 22 and 25. These two resistors are ofsufliciently high value to develop a large voltage drop across them dueto the slight amount of grid current flowing in tube T2. The. spacecurrent of tube Tzflowing through the common cathode load IIJ-III2develops sufiicient voltage across resistor It] to bias the grid of tubeT1 below its plate-current cut-01f value, the bias voltage being appliedthrough grid resistor I3. With no signal input, tube T1 is then notconducting.

The voltages and currents at various parts of the circuit for no signalinput are shown in Fig. 2 for an interval of time represented betweenthe vertical lines I and m. Referring to Fig. 2, we have then for Zerosignal input (see curve a), zero plate current in tube T1 as indicatedby curve IpTl, a steady currentin the plate circuit of tube T2 shown atIpTZ, a small positive potential on the grid of tub'e'Tz as indicated bycurve QgTZ, a steady current through inductance I2 represented by IL,and zero output as indicated by the output curve I). 7

During this period of no input signal the condensers 2| and 24 of Fig. 1are charged to the voltages impressed on their terminals by the voltagedrops developed across resistors 22 and 25 respectively. The totalvoltage across the two resistance-capacitance networks is thenapproximately equal to the anode supply voltage 13+, since the voltageacross the common cathode load circuit is just sufficient to bias tubeT1 to cut-off.

Now when a positive pulse (seecu-rve a, Fig. 2) is applied to the inputterminal 26, tube'Ti cone ducts and the potential on the plate of tubeT1 quickly drops by an amount equal to the voltage drop developed acrossthe plate load resistance comprising resistor l3 and potentiometer M.This fall of potential is applied to the grid of tube T2 throughcondensers 2! and 24 thereby biasing the tube T2 to a potential well"below its plate- =current cut-off value. At this point then tube T1 isconducting and tube T2 is not conducting.

The potential on the grid of tube T2 remains below the plate-currentcut-off value until the condensers 2i and 24 have sufficientlydischarged through their respective shunting resistances '22 and 25 tobring th potential on the grid of tube T2 up .to its cut-on value.

The length of time that the grid of tube T2 remains below its cut-ofivalue is determined by the time constants of the RC networks l9 and 20and by the setting ,of contact arm 23 of potentiorneter I 4 the positionof .arm 23 determining the .eiTective time constant of the couplingnetworks. The adjustment of the time interval willbedescribedlater.

When the grid .of tube T2 reaches its cut-off value (indicated in curv.512 y the dashed line "0. the system regenerates; that is, tube 1'2becomes conducting and tube'Ti is again cut-.off by the large negativebias developed across the cathode circuit resistance by thespace currentof tube T2. When the plate .current .of tube T; is cut .01? its platepotential immediately rises to substantially that of the supplypotential 113+. This increase in potential is also applied to "the gridof tube T2 through the coupling network condensers 2| and 24 causing asudden increase .in the plate .Current of tube T2. This high positivepotential on the grid of T2soon ialls to .the original small positivepotential 'by virtue of the grid current of tube T2.

However, during the instant the plate current of tube T2 suddenlyincreases from .zero .to the large value due to the high positivepotential .on its grid there is generated in the differentiating circuit'li-I-Z a high voltage of short duration. The magnitude of this voltageis, of course, proportional to the rate of change of space current inT2. This voltage developed across inductance l2 at this particularinstantap earsas a positive pulse at output terminal 21. There ,is thenenerated in inductance 12 a voltage at the time the conduction changes,from one tube to the other; however when the conduction changes ,fromtube T2 to tube T1 there vis only a relatively small change in currentthrough inductor 1.2 and .001 seguently only a very small negative pulseis then developedat the output terminal .21.

The voltage ,and current conditjonsjin the various parts of .the circuitfrom the time of the applied pulse at the input terminal '26 to the timewhen the circuit returns to its steady psi-signalinput state are givenin Fig. 2 between the vertical lines 112 and n. In this portion ofFig.2, the position of the input pulse is shown on some a. and thechanges that occur in those parts of the circuit, previously describedfor the interval lto m, are shown from the time of application .015

plication of apulse 1 stan't of network 4 the pulse until the grid oftube T2 returns to its steady small positive potential.

Curve e T2 clearly illustrates the drop of potential on the grid of tubeT2 at the instant the positive pulse occurs. The resultant change inconduction of tubes T1 and T2 is given at IpTl and IpTZ respectively,while at It the change in current through inductance =12 is indicated,the very small negative pulse resulting from the decrease in current incoil l2 being shown in curve I). During the interval represented betweenlines m and n of Fig. 2, the gradual rise of the grid potential of tubeT2 from the large negative potential to the .cut-off .value c. 0. (dueto the discharge of condensers 2| and 24 of Fig. 1) is illustrated 'ZtGgTZ. This curve also shows the sudden rise in grid potential at theinstant the grid of tube T2 reaches the plate-current cut-off value.

The resulting rise in plate current of tube T2 is given by curve IpTZ.Curve IL shows the sudden increase of current through inductance l2, andthe position of the positive output pulse is given in .curve b at theinstant n.

it is apparent then from Fig. 2 that the time taken for the grid of tubeT2-to rise from its'highly negative value to its cut-off valuedetermines the time interval between the applied pulse and the outputpulse of the circuit of the present invention. ,As previously stated,the time that the grid of tube T2 remains below its cut-off value isdetermined by the time constants of the coupling networks l9 and 20, andby the position of adjustable contact arm 23 of potentiometer M. Thevariation of the time interval between apto the input terminal 26 andthe generation of the output pulse at -'termin al 21 is accomplished bymeans of the arrangement of the resistance-capacitance networks 1'9 and2-11. In the preferred arrangement of these networks the time constantof network I9 is much less than that of network 20. .In addition, resistor "22 is much smaller than resistor 25. Thus when potentiometerarm 23 is at the plate end of potentiometer 14, no voltage is applied tonetwork 19 from the potentiometer and the time constant of network 20predominates, for the network I9 has little efiect upon the rate ofvoltage built-up on the grid of tube T2 since the voltage acrosscondenser 21 is small relative to that across condenser 24. When thecontact arm .23 is at the opposite end of potentiometer 14 the voltageacross the potentiometer resistance is applied to network 9. andconsequently the voltage cross condenser 21 is large and the time con-19 practically co trols the interval between the applied pulse and theoutput pulse. Intermediate positions of arm '23 will then vary theduration of the interval'betweena short e delay time govern d primarilyby the network I15, and a lo er elay ime n e ime co stant of network2.1) prevails.

"By the prop r sel n o e time c n t nt of networks 19 and 2D and a sutable ratio of potentiometer l4 resistance to the total resistance ofthe plate circuit of tube T1 the interval between the app ed p se andthe e ayed o pu pulselm y'be eas y a ju ted by a ioe e ontrol over ,awide ran e.

'Whilethe invention h e n d scr bed for one par icular embod mentaccordin to Eli 1, it will appa n to hose skil ed in thea t tharnodifications of the circuit may be made without devia ing f om t egeneral pr nciples-of the invention. For in ance Fi .3, whichillustrates a l ernative arrangement of a portion of the circuit of(switch 28 in right-hand position) or through a suitable potentialsource (switch 28 in left-hand position).

In practicing this invention in 'accordancewith the embodimentillustrated in Fig. 1, a pulse delay from approximately 4 to 400microseconds. values of the circuit elements were approximately asfollows:

section of a type 7N7 tube Although this invention has been describedwith particular reference to the embodiments of disclosure but only bythe scope of the appended claims.

I claim: 1. A pulse vibrator circuit of the type 2. A pulse vibratorcircuit employing first and second tubes and the grid of said secondtube, the first of said networks comprising fixed resistance and fixedcapacitance, the second of said networks comprising a condenser and anadjustable resistor.

3. A pulse delay system, comprising a singlecycle multivibrator of thetype employing a pair of inter-coupled vacuum tubes having at least thegrid of the second tube, and means for applying a voltage of variablesaid networks so as to provide a substantial range of adjustment of thetime interval between said pulses.

5. A pulse delay system, comprising a multivibrator circuit employingfirst and second tubes having triode elements regeneratively interforefiecting a delay between said input pulse and said output pulse, saiddelay-efiecting means time delay network having a relatively small timeconstant and a second time 6. A pulse delay system, comprising amultivibrator circuit of the type employing a first and a second tuberegeneratively intercoupled to proond tube for the grid circuit of sa1dsecond tube, network comprising resistance and capacitance elements andhaving a relatively large time constant, and means for applying avariable v.portion of the anode voltage change of said firstitiibe :tosaid ifirstne'tworik .so as to vary the relative effectiveness of saidnetworks and thus vary the "time delay'between saidinputpulse andsaid'voltage ,pulse. a

"Z. In a system of the type described, .a first electron tube "having atleast .triode elements, a source of anode voltage, aresistorconnectedbetween Ithe anode .o'f said tube .and said source, va second electrontube having at least triocle elements, a pair or condensers seriallyconnedted between "the anode of said first tube and the grid of saidsecond tube, a resistor connected between the junction of saidcondensers and an adjustable tap :on said first-mentioned resistor so asto provide afirst delay network, the values of said elements of saidnetwork being such as to impart to said "network a relatively smallZtimc constant, and a resistor connected in shunt with the secondcondenser 'so as to provide a second time :delay network, the values of"thela'tter elements' be'ingsuch as .to impart to said secondntwork'arelative'ly large time constant.

8 REFERENCES orzrsn The following reierenees'are of record in the fileof this =pa'tent:

5 UNIT-ED S'IlATE'S PATENTS Number Name Date 2,050,059 K0611 Aug. 4,1936 2,118,626 iSmith May 24, 1938 2,193,850 -i-mdrieu Mar.19, 1940 10.2,22s;n0s Cawe'in Dec. 31, 1940 2262,8138 Delorai'me eti'a1.- .Nov. 1-8, 1931 2,266,401 Reeves Dec. '16, 1941 :2;266;668 :Uubbs iDec. 16,19412,212,070 Reeves Feb. 3, 1-942 15 2294368 Hadfield S'ept. 1,:194212,366,076 Wilbur .Dec. 26, 1944 2,373,145 :Sensiper et :al Apr. 710,1945 2502,9 15 Schroeder June 25, 1946 20 FOREIGN PATENTS Number CountryDate 356,111 Grea'tBfitain AugfQA, I931

